Study On Aging Characteristics Of Typical Plastics And Microplastics

Plastic products have the characteristics of light weight,low density and durability.They are widely used in various fields such as life,production,construction and aerospace.The influx of waste plastics into the environment has caused a series of plastic and microplastic pollution problems.Plastics and microplastics exist in various environmental media for a long time.After long-term aging,their surface morphology,chemical composition,crystallinity and thermal stability and other aging characteristics have undergone a series of changes.Therefore,this paper studies the aging characteristics of typical plastics and microplastics,and discusses their interaction characteristics with pollutants.The main research contents are as follows:1.Research on the aging characteristics of waste plastics in landfillTaking the waste plastic collected from Shanghai MSW landfill as the research object,it is found that the landfilling waste plastic has undergone degradation changes by Fourier Transform Infrared Spectroscopy(FTIR),Differential Scanning Calorimetry(DSC),Scanning Electron Microscopy combine with Energy Dispersive Spectroscopy(SEM-EDS)and the mechanical universal testing machine.Compared with the original plastic samples,these degradation characteristics show that the collected waste plastics produced C=O,-OH oxygen-containing functional groups and the surface roughness increased.The surface water contact angle also decreased from 102.2° to 81.0°,which indicating that the waste plastics the hydrophobic properties decreased.Meanwhile the mechanical properties of waste plastic also tended to weaken with increasing landfill age.The information obtained from the energy spectrum analysis is consistent with the FTIR results.The increase in the oxygen content of waste plastics leads to a decrease in C/O,and the C/O tends to decrease continuously with the increase of landfill age.At the same time,the surface of waste plastic also detected the presence of trace elements such as Al,Fe,and Co,which is very likely to be the release of plastic additives.The mechanical properties of waste plastics decrease and the surface morphology is degraded and weathered seriously,which greatly promotes the generation of microplastics.In addition,the oxygen content of waste plastics in landfill is very low and grows slowly.Thus it has little impact on the recovery of hydrocarbon fuels by pyrolysis.2.Study on the characteristics and adsorption behavior of typical microplastics with long-term accelerated simulated agingThe aging process of three microplastics of polyethylene(PE),polystyrene(PS)and polybutylene terephthalate-adipate(PBAT)in natural environment is simulated by ultraviolet rays and alternating heat and cold treatment.The relationship between the aging characteristics of microplastics and aging time was discussed,and the adsorption behavior of pollutants onto microplastics before and after aging was studied.The surface morphology,chemical composition,crystallinity and thermal stability of microplastics changed regularly with aging time,especially the linear fitting degree of PE carbonyl index(CI)with aging time reached 0.99.In the aging experiment,the change of CI can be more accurately estimated.It should be noted that PE reaches the oxidation equilibrium under the accelerated aging of 120 d,and the CI no longer increases with the aging time.The results of adsorption experiments showed that the adsorption capacities of the three microplastics were improved to varying degrees after aging.And it was also confirmed that salt ions(Na Cl)and dissolved organic matter(DOM)in the environment would reduce the adsorption capacity of microplastics.3.Study on aging characteristics of typical plastics and degradable plastics and the toxicity of microplastics onto plantsThe aging process of one conventional plastic and four degradable plastics was studied under the outdoor natural conditions and the indoor simulated natural environment,respectively.The research results show that biodegradable plastics can indeed be degraded into plastic fragments under abiotic conditions.In particular,conventional PE plastics have severely fragmented,forming microplastics <5 mm.Comparing the degree of plastic aging under indoor and outdoor conditions,it was found that UV light is a key environmental factor in the evolution of macroplastics to microplastics.During the aging process,the oxygen-containing peaks of the five types plastic sheets were very different.The C=O peaks of PE and PE-St were enhanced,while the C=O absorption peaks of the other three degradable plastics gradually weakened.At the same time,in the toxicological experiments of microplastics on plants,the toxic effect of conventional PS was greater than that of degradable PBAT.And it had an inhibitory effect on the chlorophyll content and biomass accumulation of plants.Overall,the inhibitory effect on soybean was significantly higher than that of wheat.In addition,the toxic effects of microplastics on plants also depend on their particle size.